Use newer PHP version in Travis config, add Nix to build matrix

.travis.yml

@@ -1,14 +1,30 @@
 # Note: all environments run nodejs, so set language to PHP so we can lint all of the PHP functions
 language: php
+
 php:
-  - "5.3"
+  - 7.2
+
 before_script:
   - npm install
   - make
+
 script:
   - make check_changes
   - make test
 
 branches:
   only:
     - master
+    - travis
+
+env:
+  global:
+    - secure: "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"
+
+matrix:
+  include:
+    - language: nix
+      before_script:
+      script: nix-build --argstr handlebarsSpecVersion $TRAVIS_BRANCH | tee result.txt
+      after_success: cat result.txt | cachix push jbboehr-ci
+